In rats, intraventricular injection of morphine and beta-endorphin decrease the turnover rate of acetylcholine (TRACh) in the cortex, hippocampus, N. accumbens and globus pallidus, but not in the striatum. Beta-endorphin is approximately 100 times more active than morphine both in inducing analgesia and catalepsy and in decreasing the TRACh. Naltrexone, a narcotic antagonist reverses the action of beta-endorphin and morphine. Intraseptal injections of morphine and beta-endorphin are not able to induce analgesia or catalepsy, but decreases the TRACh in the hippocampus. Intraseptal injections of naltrexone curtail the decrease of hippocampal TRACh caused by intraperitoneal morphine. These results suggest that only certain cholinergic neurons are regulated by opiate receptors. Specifically they demonstrate that the septal hippocampal cholinergic pathway is modulated by opioid receptors and that this action is dissociated from the onset of analgesia. BIBLIOGRAPHIC REFERENCES: Moroni, F., Cheney, D.L. and Costa, E.: Beta-endorphin inhibition of ACh turnover in nuclei of rat brain. Nature, in press, 1977. Moroni, F., Cheney, D.L. and Costa, E.: Inhibition of acetylcholine turnover rate in hippocampus by intraseptal injection of beta-endorphin and morphine. Naunyn-Schmied. Arch. Pharmacol., in press, 1977.